Exercise 1: Put the verbs in the simple present tense 1. Mothers often (tell) their children stories at bedtime. 2. He (brush) his teeth before he (go) to bed. 3. Every year they (go) to the countryside on holiday. 4. Lan usually (not/watch) T. V in the evening. 5. My friends always (wish) to become a teacher. 6. What time your father (go) to work ? 7. We always (understand) what the teacher (explain). 8. He (live) in Thai Nguyen in summers. 9. I usually (go) to school by bus. 10. What program he (watch) in the afternoon ?

1. Mothers often tells their children stories at bedtime

2.  He brushes his teeth before he goes to bed

3. Every year they go to the countryside on holiday.

4. Lan usually don't watch T.V in the evening.

5. My friends always wishes to become a teacher.

6. What time your father goes to work ?

7. We always understand what the teacher explains.

8. He lives in Thai Nguyen in summers.

9. I usually go to school by bus.

10. What program he watches in the afternoon ?

. a function is a relation in which each input has only one output. in the relation , y is a function of x, because for each input x (1, 2, 3, or 0), there is only one output y. x is not a function of y, because the input y = 3 has multiple outputs: x = 1 and x = 2.